A generic belt tensioner is disclosed in DE 94 05 834 U1 or U.S. Pat. No. 5,782,423 A, for example. Both documents describe a belt tensioner in which a pyrotechnically drive generates a compressed gas which applies pressure on a curved toothed rack which is in engagement with a pinion.
GB 2 323 016 A discloses a belt tensioner in which a sector gearwheel driving a pinion is driven by mass bodies acted upon with pressure, which are in the form of balls.
WO 03/082640 A1 likewise describes a so-called ball tensioner in which in a case of activation a pyrotechnical drive drives the balls into recesses of a drive wheel and thereby causes the drive wheel to rotate.
EP 0 628 454 A1 discloses a belt tensioner in which a ring gear of a planetary gearing is provided as the drive element and is coupled to a sun wheel via a plurality of planet wheels. The sun wheel, in turn, is adapted to be coupled to a belt reel. The ring gear includes a wing extension which is mounted in an annular channel surrounding the ring gear. Communicating with the channel is a gas generator which upon actuation generates compressed gas which applies pressure on the wing extension and thereby drives the ring gear.
From DE 103 42 283 A1 a belt tensioner is known in which as a drive unit a pyrotechnical propellant charge is provided. This propellant charge generates a compressed gas which acts upon the piston of a piston/cylinder unit that is guided in the cylinder so as to be longitudinally displaceable. The piston is coupled to a toothed rack which drives the shaft of a belt retractor via a pinion, in order to retract a slack in the belt webbing in a restraint case.